1. Field of the Invention
The present invention relates to an image pickup apparatus and a camera.
2. Description of the Related Art
In conventional digital cameras, the following two types of auto focusing (AF) have been realized.
The first type is a type in which, apart from an image pickup element, a sensor for auto focusing has been imparted. A typical example of this type is a phase-difference type AF which is used in a single-lens reflex camera. A merit of this type is that a light beam which has passed through a taking lens is used and a problem of parallax is solved, and a focal shift is detected by a ranging signal once, thereby making it possible to focus the taking lens on an object, and shortening time till focusing.
On the other hand, in this type, it is necessary to dispose a means for dividing or switching an optical path, between the taking lens and the image pickup element. Furthermore, an optical system for AF is necessary between the means for splitting or switching the optical path and the sensor for AF. Firstly, there is an increase in a size due to securing of a space for the means for switching the optical path and securing of a space for the optical system for AF and the sensor for exclusive use. Moreover, as a further demerit, in a case of disposing the means for switching the optical path, a time lag occurs due to switching with a switching mechanism, and in a case of disposing the means for dividing the optical path, there is a loss in an amount of light due to optical-path splitting.
The second type is a type in which, an output of the image pickup element is used. A typical example of this type is a contrast AF in which, a so-called compact digital camera, and a video camera have been used. A merit of this type is a merit of space, as the image pickup element and the AF sensor are integrated, and a point that the number of structural members is fewer.
On the other hand, a demerit of this type are points that it is necessary to compare a multiple number of ranging signals, and that it takes time till focusing, due to wobbling. Furthermore, blurring of an image due to wobbling is captured, and according, an image quality is impaired. This trend is more remarkable as the number of pixels becomes larger.
Furthermore, in recent years, for a single lens reflex camera, which includes an optical finder in which, a quick return mirror and a roof prism are used, an interchangeable lens camera premised on an electronic view finder which does not require the quick return mirror and the roof prism, has already been released. In this interchangeable lens camera, it has been sought that both, a still photography and a video photography, have a high quality. Particularly, in such camera, an AF, in which, while having merits of the two types mentioned above, the demerits are eliminated, has been sought.